It may be advantageous for laser processing to determine or to know precisely the beam profile of a laser beam, e.g., the position-dependent intensity distribution or power distribution of the laser beam perpendicular to the direction of propagation of the laser beam. For example, it can be advantageous to know the beam profile at or near a processing plane, in which the laser beam is typically focused for the processing. A workpiece may, for example, be arranged in or near the processing plane in a laser processing machine or a powder layer to be irradiated may be arranged in a processing machine for producing three-dimensional components. In the case of a powder material, a laser beam in such a processing machine is focused on a layer of the powder material, typically in the form of a metal powder, so the powder material fuses locally to produce a layer of the three-dimensional component (“laser metal fusion”, LMF).
Ensuring an optimally stable process requires that the scanner device or an irradiation device having such a scanner device provide a defined, reproducible beam profile (laser spot) in the powder bed or on the powder layer irradiated by means of the laser beam. For this purpose, the beam profile may be carried out upon or during the start-up of the processing machine with the aid of a special measuring device, which is introduced into the processing device near the processing plane. Since the processing chamber is normally inaccessible from the outside, the time invested in assembling and disassembling the measuring unit, as well as in the actual measurement, is considerable and may amount to several hours. Since the measuring unit requires considerable installation space, it is also not possible to carry out the determination of the beam profile during the operation of the processing machine.
A device for measuring the intensity profile of a laser beam, which has a semi-transparent deflection mirror arranged in the beam path of the laser beam for coupling a small portion of the radiated power of the laser beam out to a spatially-resolving detector, has become known from JP H02-038931 A. A deflection mirror, which is already provided in the beam path for deflecting the beam, is preferably used for such purpose.
A device for determining geometric parameters of a laser beam, which comprises a beam diagnostic device and an optical system designed to focus a laser beam in a processing area, is described in DE 10 2015 001 421 A1. A reflector element is positionable in a positioning area between the optical system and the processing area and includes a first semi-reflective surface, the first surface being curved and the curvature of the first surface being identical to an average curvature of a wave front of the laser beam focused by the optical system in the positioning area of the reflector element. The reflector element may be an optical lens having a spherical surface, for example, a plano-convex lens or a concentric meniscus lens. The beam diagnostic device may comprise a device for focusing coupled-out radiation and a spatially resolving sensor.